Human errors and "systems failures" are blamed for a mix-up at a Leeds hospital which led to mixed race twins being born to a white couple.
A report was commissioned two years after the mistake at the IVF department at Leeds General Infirmary.
Professor Brian Toft says the two sperm samples were not properly identified although it was not possible to say at what point this happened.
However, a number of weaknesses were found in the embryology laboratory.
Professor Toft's report reveals that other mistakes were made in the department.
One involved the loss of embryos following a failure to check liquid nitrogen in a cryogenic freezer.
Another saw the disposal of embryos following an administrative failure.
The report includes recommendations to the Department of Health, the Human Fertilisation and Embryology Authority (HFEA) and the Leeds NHS Teaching Hospitals Trust.
But Professor Toft makes it clear that changes have been made since the mistakes took place.
He said: "The starting point for this review was that patient safety is paramount.
"Patients need to be confident in the assisted conception treatments they are receiving.
"During this review we identified a number of potential vulnerabilities and weaknesses in the regulatory procedures and clinical systems that were in place
when the incidents occurred."
The government's Chief Medical Officer Sir Liam Donaldson said: "The mistakes detailed in this investigation were enormously distressing to the patients involved and their families.
"Lessons will be learned from what happened so that we can reduce the chance that anything like this will happen again."
The HFEA said it had now carried out 85% of Professor Toft's recommendations.
- double-checking of patient identification at all stages of treatment
- unannounced inspections of clinics
- improved recruitment and training of inspectors and staff
- setting up an alert system to ensure timely investigation of all incidents
The authority had also designed a new code of practice for clinics, setting
out required standards.
HFEA chairwoman Suzi Leather said: "This mistake has caused great emotional
turmoil and pain.
"We owe it to every patient and every baby born to make sure that the HFEA is doing everything possible to minimise the risks.
"Like other areas of medicine, it is not possible to eliminate all risks, but we have improved safety in clinics and this will continue. I'm pleased that the significant progress we have made has been recognised in this report."